Stormwater detention temporarily stores runoff and releases it over time through a controlled outlet.
Definition
Stormwater detention is temporary storage that slows runoff and releases it through an outlet or other controlled route. Facilities may include basins, tanks, or constructed storage areas, with configuration and performance determined by site conditions and project criteria. Design work may involve estimating inflows, evaluating storage and outlet behavior, coordinating grading and utilities, and documenting operations or maintenance needs. Firms can use different modeling methods and assumptions, so the modeled storm inputs and outlet conditions should be clear. Detention generally aims to manage the timing or rate of discharge; it does not necessarily keep all water on site or remove pollutants by itself. It differs from retention, which commonly refers to holding water through infiltration, evaporation, reuse, or other means. Neither term alone establishes maintenance responsibility or guarantees performance under every event.
How owners use it
- Evaluate temporary storage and controlled release as part of a drainage design.
- If a facility receives 7 acre-feet and releases 5 during the modeled period, the stored difference is 7 - 5 = 2 acre-feet.
- Coordinate basin or tank footprints with grading, utilities, access, and site constraints.
- Document outlet assumptions and expected inspection or maintenance responsibilities.
